Alumina extraction from raw Hadong kaolin with sulfuric acid was studied to obtain relatively pure alumina. Factors as acid concentration, heating temperature and conditions of ammonium alum crystal formation from extracted solution are also surveyed and most of iron oxide in kaolin is eliminated in crystallization of ammonium alum. Pure crystal obtained from the extracted solution with ammonium sulfate is relatively free from iron containment in mother liquor. Alumina in ammonium alum crystal is converted to gibbsite form after complete hydrolysis in ammonia gas.